Hierarchical Routing in Computer Networks || Routing Algorithms

Summary

This transcript discusses hierarchical routing in large networks, addressing the challenges of network scalability and router efficiency. As the network grows, the number of routers and the size of their routing tables increase, leading to higher memory and bandwidth consumption. Hierarchical routing divides the network into regions, with routers within a region aware of each other but not of routers in other regions. Gateway routers are used to facilitate communication between regions. This method reduces the burden on individual routers, making it easier to manage large networks by optimizing memory use and minimizing bandwidth consumption.

Takeaways

• 😀 Hierarchical routing helps manage large networks by breaking them into smaller regions or subnets.
• 😀 As the size of a network increases, the number of routers and the size of routing tables also grow, making it harder for routers to handle traffic efficiently.
• 😀 Each router in a region only knows how to route traffic within that region, not to routers in other regions.
• 😀 Gateway routers bridge the gap between regions by storing information about routers in other regions, facilitating inter-region communication.
• 😀 A router in one region forwards traffic to a gateway router when it needs to send a packet to another region.
• 😀 Hops in a routing table refer to the number of routers or links the packet must pass through to reach its destination.
• 😀 In hierarchical routing, each region has its own set of routers and gateway routers to manage the traffic within that region and beyond.
• 😀 The main advantage of hierarchical routing is that it reduces the size and complexity of routing tables by limiting the scope of routing decisions to specific regions.
• 😀 A router uses its routing table to determine the best path for sending packets, choosing between internal and gateway routers based on the destination.
• 😀 The hierarchical approach allows for more efficient management of large-scale networks, minimizing the need for excessive memory and bandwidth for routing information.

Q & A

What is the main issue that hierarchical routing seeks to solve?

Hierarchical routing seeks to solve the issue of large routing tables in expansive networks. As network size increases, the number of routers grows, causing the routing tables to become too large and difficult to manage efficiently, requiring more memory and bandwidth.

How does hierarchical routing divide a large network?

Hierarchical routing divides a large network into smaller regions, each containing a set of routers. These regions, also referred to as subnets, help reduce the complexity of managing large networks by organizing the routers into manageable groups.

What is a gateway router and what role does it play in hierarchical routing?

A gateway router is a router that has information about routers in other regions of the network. It acts as a bridge, enabling communication between routers in different regions. For example, if a router needs to send a packet to a router in another region, it sends the packet to the gateway router, which handles the inter-region communication.

Can routers within the same region communicate directly with each other?

Yes, routers within the same region can communicate directly with each other. Each router knows how to route packets to other routers within its region, but it does not have information about routers in other regions.

What is the benefit of using hierarchical routing in large networks?

The primary benefit of hierarchical routing in large networks is scalability. By dividing the network into regions and using gateway routers for inter-region communication, it becomes easier to manage the routing tables, reduce complexity, and optimize the traffic flow.

How does a router in one region send a packet to a router in another region?

To send a packet to a router in another region, the source router forwards the packet to a gateway router. The gateway router then handles the routing to the destination region. For example, a router in Region 1 will send the packet to a gateway router in Region 1, which will then route it to the destination router in another region.

What happens when a router needs to send a packet to a router in a different region?

When a router needs to send a packet to a router in a different region, it forwards the packet to a gateway router in its region. The gateway router then forwards the packet to the appropriate router in the destination region, ensuring that the packet reaches its final destination.

What is the hierarchical routing table, and how does it differ from a normal routing table?

A hierarchical routing table is structured to represent regions and routes between them, in addition to local router routes. Unlike a normal routing table that only contains information about routers within the same region, a hierarchical table includes routes to external regions via gateway routers.

What role does the gateway router play in reducing the size of routing tables?

The gateway router reduces the size of routing tables by consolidating the routing information for routers in other regions. Routers do not need to know the full routing information for all routers in the network, just the gateway router that can forward packets to other regions, making routing more efficient.

Why are hops important in hierarchical routing, and what do they represent?

In hierarchical routing, hops represent the number of routers (or links) a packet must pass through to reach its destination. A hop can refer to either a router or an edge (link) between routers. Reducing the number of hops helps improve the efficiency of packet routing across regions.